1. Field of the Invention
The present invention relates to a hydraulic actuator system adapted for the repetitive movement of a load having a given mass such as a conveyor or an anti-rolling apparatus of or a vessel, particularly to a hydraulic actuator package having a small size and light weight which is formed by integrating each component unit of the hydraulic actuator system.
2. Description of the Related Art
A hydraulic actuator system of this type is disclosed in JP-A 8-244682 (an anti-rolling apparatus of a vessel) which has been previously proposed by the applicant.
This system comprises, as shown in FIG. 6, a variable displacement hydraulic motor 101 which uses liquid such as oil as a power medium, a weight 103 which is an inertia object and is mechanically connected to a main shaft 102 of the hydraulic motor 101, an auxiliary pump 105 for supplying operation fluid under high pressure to the hydraulic motor 101 and an accumulator 108 serving as a hydraulic source of the hydraulic motor 101 by way of a check valve 107, a tank 109 to which the operation fluid from the auxiliary pump 105 and that from the hydraulic motor 101 returns, and first and second displacement control pistons 112 and 113 which operate by way of a closed center type control valve 111 in response to an instruction issued from a control unit 110.
A pulse encoder 114 serves as a speed sensor for generating a pulse signal in response to a revolution speed of the main shaft 102 of the hydraulic motor 101, and it feeds back the pulse signal to the control unit 110. The control unit 110 outputs an operation signal to the control valve 111 so that the detected value of the shaft speed which is obtained by subjecting the pulse signal to an F/V conversion conforms to a speed instruction value, thereby varying the inclination of an inclination plate of the hydraulic motor 101 to control the capacity of the hydraulic motor 101.
With such a construction, a rolling of a vessel is detected by a sensor such as an acceleration speedometer (not shown) provided in the vessel, and a control instruction to move the weight 103 in the direction to attenuate the amount of detected rolling is supplied to the control unit 110. At this time, since an instantaneous large power needed for driving the weight 103 is discharged from the accumulator 108, the operation fluid to be supplied from the auxiliary pump 105 becomes small power.
Since a kinetic energy of the weight 103 can be collected by the accumulator 108 when the speed thereof is reduced, it is possible to drastically save energy compared with a normal hydraulic driving apparatus which changes braking energy into heat and discharges the heat. Such a hydraulic actuator system is referred to as a secondary control system.
In FIG. 6, although the weight 103 is mechanically connected to the main shaft 102 of the hydraulic motor 101 for the convenience of the illustration, the weight 103 is actually slidably mounted on a guide bar which is provided in the width direction of the vessel. The hydraulic motor 101, the auxiliary pump 105, the accumulator 108, the tank 109, etc. are mounted on the weight 103.
However, if the conventional hydraulic actuator system is employed in general use, the hydraulic motor 101, the auxiliary pump 105, the accumulator 108 and the tank 109 must be individually prepared, and they are mounted on the weight 103 or a fixed portion of the vessel, then they must be connected to one another by a communication pipe line or a connecting member, thereby needing much time and labor and causing a problem in that the entire apparatus becomes large in size and heavy in weight.
If the communication pipe line becomes long, pressure loss becomes large, which causes another problem in that extra power corresponding to the loss must be supplied.